The present invention relates to an ultrasonic probe for used in an ultrasonic diagnosis apparatus, an ultrasonic treatment apparatus, and the like, and a method of manufacturing the probe.
An ultrasonic probe is constructed with a piezoelectric member used as a main member, emits an ultrasonic wave to a target object, and receives reflection waves from interfaces between which acoustic impedance differs, thereby to image the inner state of the target object. As an ultrasonic imaging apparatus which adopts this kind of ultrasonic probe, for example, there is a medical diagnosis apparatus for inspecting inside of a human body, an inspection apparatus for the purpose of flaw detection inside metal welding, or the like.
In the ultrasonic diagnosis apparatus as the medical ultrasonic imaging apparatus, photographing techniques such as a color flow mapping (CFM) method in which Doppler shift of ultrasonic waves depending on blood flow is used to display two-dimensionally the speed of blood flow, a tissue harmonic imaging (THI) method in which a two-dimensional wave is imaged, and the like have been developed in addition to a stratigraphic image (B-mode image) of a human body. The ultrasonic probe has a form which coincides with these various photographing methods and enables transmission/reception of ultrasonic waves concerning all organs of a human body.
In general, it is demanded that the ultrasonic probe for use in an ultrasonic diagnosis apparatus can obtain an image with a high resolution with a high sensitivity. This is because small pathologies and gaps can be detected by an image capable of displaying clearly a deep part of a diagnosis target. In recent years, consideration has been taken into heightening of the sensitivity and widening of the band of the ultrasonic probe as a sensor part.
To achieve a higher sensitivity and a wider band as described above, studies are made on a composite piezoelectric member such as a structure in which a piezoelectric column or piezoelectric particles are embedded in resins. For example, structures thereof are proposed in Japanese Patent Application KOKOKU Publication No. 54-19151 and Japanese Patent Application KOKAI Publication Nos. 60-97800, 61-53562, and 61-109400 and the like, and manufacturing methods thereof are proposed in Japanese Patent Application KOKAI Publication Nos. 57-45290, 58-21883, 60-54600, 60-85699, 62-122499, and 62-131700 and the like.
An ultrasonic probe using a composite piezoelectric member disclosed in these references has merits that the acoustic impedance decreases close to the impedance of a living body and that the electromechanical coupling factor in the structure of 1-3 type, 2-2 type, or the like increases in comparison with a thin plate. This is because PZE-based piezoelectric ceramics having a large dielectric constant and a large electromechanical coupling factor k33 are used mainly.
Meanwhile, an ultrasonic probe using a composite piezoelectric member has a problem that the electromechanical coupling factor improves less compared with a reduction of the dielectric constant due to inclusion of resins. In practice, the composite piezoelectric member is used only for a single-type mechanical probe, an annular array, or the like which has a large element area. Hence, trials have been made to solve this problem by using a solution-based piezoelectric single-crystal (Japanese Patent Application KOKAI Publication No. 09-84194).
To realize an ultrasonic probe with high sensitivity and a wide band, there has been a method of forming a composite piezoelectric member 30 made of solution-based piezoelectric single-crystal 32 and resins 34 and 36, like the array-type probe shown in FIG. 1A. However, formation of this composite piezoelectric member 30 has a problem of an error in cutting work. That is, solution-based piezoelectric single-crystal 32 generally has low breakdown resistance and is fragile, so a problem occurs in that chipping is caused in cutting work for forming a kerf 38 shown in FIG. 1B into an array-like shape. This chipping causes characteristic deterioration and cracks in an element, thereby causing errors.
Hence, we have proposed a structure as shown in FIG. 1D (Japanese Patent Application KOKAI Publication No. 2000-14672) as an ultrasonic probe using single crystal of this kind, and have tried to improve the probe manufacture yield. FIG. 1D shows a cross-sectional view structure of an array probe using a single-crystal vibration element. Electrodes 4 and 5 are formed on both sides of the single-crystal vibration element 1, and a backing material 2 is provided on the lower surface of the vibration element 1. In addition, acoustic matching layers 3a and 3b are formed on the single-crystal vibration element, so that the single-crystal vibration element 1 and the matching layers 3a and 3b are subjected to array processing. The array pitch of the array probe is about 0.1 mm in case where the pitch is small. Further, transmission/reception of an ultrasonic wave is carried out through an acoustic lens 8 provided on the acoustic matching layer 3b. The electrodes 4 and 5 formed on the both surfaces of the single-crystal vibration element 1 are connected to a cable through FPCs 6 and 7 and thus connected to a diagnosis apparatus (omitted from figures). In the structure shown in FIG. 1D, the FPC 6 is joined to the vibration element by an epoxy-based adhesion throughout the all surface of the vibration element, by extending the conductive layer of the FPC so as to correspond to the area of the vibration element. Metal Cu is generally used as the conductive layer. FIG. 1E shows a conductive layer at a lower portion of the signal FPC shown in FIG. 1D, viewed from the single-crystal vibration element 1. The conductive layer 6a′ of the signal FPC shown in FIG. 1D is led like a hound's tooth check as shown in FIG. 1E. This array structure is prepared in the manner explained below. Electrodes 4 and 5 are formed on the single-crystal vibration element 1 having an integral shape. A vibration element to which a FPC is adhered is adhered to the backing member 2. Acoustic matching layers 3a and 3b are formed, and thereafter, a dicing saw is used to cut them from the side of the matching layer. Thereafter, the acoustic lens 8 is formed on the acoustic matching layer 3, and preparation is thus completed.
However, a problem has occurred in that cracking and chipping occur in some cases at the dicing edge part of the surface where the FPC of the single-crystal vibration element is adhered, if the above manufacturing method is adopted, a FPC whose conductive layer is extended to correspond to the area of the single-crystal vibration element is adhered to the entire surface of the vibration element by an epoxy-based adhesion, the vibration element is adhered to a backing member by an epoxy adhesion, an acoustic layer is formed on the vibration element, and array processing is thereafter carried out by a dicing saw. This is considered to occur because the piezoelectric single-crystal having weak mechanical strength and the conductive layer having a deteriorated cutting characteristic are cut simultaneously. In addition, burs from the conductive layer which are created during processing roughen the cutting surface of the single-crystal vibration element, and cutting wastes caught under a blade are factors which lower the cutting characteristic. These cracking and chipping of the single-crystal vibration element are difficult to suppress even if the processing conditions are adjusted. Large cracking causes a disconnection error and lowers the manufacturing yield while small cracking expands during use and may cause a market accident. Also, chipping reduces the electrode area of the vibration element processed into a strip-like shape, so that not only characteristic deterioration is involved but also characteristic variants increase between array elements. Since several tens to several hundreds of array elements are used, characteristic variants between array elements influence the image quality of a stratigraphic image.